1. Field of the Invention
The invention is related to an optical device and a light source, and more particularly to a light guide plate and a light source module.
2. Description of Related Art
Conventional side incident type light source modules use a light guide plate to guide a light beam emitted by a light emitting device disposed at the side of the light guide plate to the front of the light guide plate, to form a surface light source. Generally, when the light beam emitted by the light emitting device enters the light guide plate through the side of the light guide plate, it will continuously be totally reflected by the top surface and the bottom surface of the light guide plate, and is limited in the light guide plate. However, microstructures disposed in the surface of the light guide plate could disrupt the total reflection, causing the light beam to hit the top surface at an angle smaller than the critical angle, and thus passing through the top surface.
Even though the microstructures could disrupt the effect of total reflection, through the utilization of microstructures, most of the light beam will exit the top surface of the light guide plate obliquely, and not exit the top surface perpendicularly. In order to cause the light beam to exit perpendicularly, a prism sheet is disposed on the top surface of the light guide plate of a conventional light source module, so the advancement of the light beam will be guided directly above. In addition, the prism sheet will reflect the light beam with part of the advancement angle back to the light guide plate, such that the light beam could be reused again. However, when the light beam passes through an additional prism sheet and is totally reflected to the light guide plate, light is wasted, thus reducing the brightness provided by the light source module.
Taiwan Patent No. I282021 discloses microstructures of a light guide plate, and the microstructures are arranged repeatedly on a bottom surface of the light guide plate. Taiwan Patent No. I296352 discloses a light guide plate with a plurality of annular structures. The light guide plate has a first annular structure and a second annular structure. The first circular structure and the second circular structure have different widths of bottom surfaces. The microstructure could be located on the bottom surface of the light guide plate. U.S. Pat. No. 6,454,452 discloses a light guide plate where a bottom surface thereof has wedge shaped grooves, wherein included angles between inclines and the bottom surface of the grooves are 43 degrees, 45 degrees, and 47 degrees. Taiwan Patent No. M321111 discloses a light guide plate with a certain regular arrangement of microstructures. U.S. Pat. No. 6,612,722 discloses a light guide plate with microstructures. U.S. Pat. No. 6,834,973 discloses a light guide plate with a bottom surface having micro-reflective structures. Taiwan Patent No. I222533 and U.S. Pat. No. 6,967,698 disclose a liquid crystal display apparatus including a surface light source apparatus. Taiwan Patent Publication No. 200530632 discloses a light guide plate.